1. Field
The disclosed embodiments relate to a system for opening and closing a flap or door of the landing gear well or casing of an aircraft to allow the door to open by the minimum amount when the landing gear is down.
The disclosed embodiments find applications in the field of aeronautics and, in particular, in the field of doors that close the landing gear well of an aircraft.
2. Brief Description of Related Developments
A landing gear well is a housing intended to accommodate a landing gear of an aircraft, particularly when the landing gear is placed under the fuselage of the aircraft. This gear well is generally closed by one or more doors. There are various kinds of door:
main doors which open to allow the landing gear to be lowered and which close again once the gear is down, and
secondary doors, for example front landing gear doors, which open to allow the landing gear to be lowered and remain open as long as the gear is down.
A landing gear door, also sometimes known as an undercarriage door, usually comprises a panel, fixed to articulating arms. In general, these articulating arms are articulated to the structure of the aircraft about a pivot pin which is offset toward the inside of the gear well with respect to the panel. When the landing gear is being lowered, the panel is pivoted toward the outside of the fuselage by means of a connecting rod positioned between the panel and the structure, inside the gear well.
In order to preserve the aerodynamics of the fuselage, the pivot pin is positioned inside the gear well. Again, for aerodynamic reasons, the secondary doors have to open as little as possible to allow the landing gear to pass through while at the same time preserving aerodynamic continuity.
At the present time, each secondary door is connected to the landing gear by a direct connection. This direct connection consists of a connecting rod attached, at one end, to the landing gear, for example to the gear leg or to the landing gear strut and, at the other end, to the door. This connecting rod allows the door to be operated directly as a function of movements of the landing gear. Thus, as the landing gear is retracted, the very fact that the landing gear is rising up inside the gear well closes the door. Similarly, as the landing gear is being lowered, this direct connection opens the landing gear door by pushing it toward the outside of the fuselage. More specifically, as the landing gear is being lowered, it rotates about a pivot pin, causing a translational movement of the connecting rod which pushes the door into its open position. A direct connection such as this therefore means that the lowering of the undercarriage and the opening of the door can be instigated at the same time.
For a large-sized aircraft the landing gear is larger in size than a landing gear for an aircraft of conventional size. As a result, the gear well is larger, and, in particular, longer, thus entailing the use of longer doors and/or of a greater number of primary and secondary doors in order to close the gear well.
The increase in the number of doors leads to there being a greater number of door opening and closing systems and therefore to an increase in the volume and mass of the doors. In addition, the increase in the number of doors increases the risk that a door opening and closing system might fail.
The increase in the size of the doors leads to an increase in the mass of each door and to a change in the center of gravity. Now, fitting a conventional control connecting rod to a large-sized door can be done only close to the rear edge of the door, that is to say at one end of the door rather than in the middle of the door. Specifically, the connecting rod cannot be fitted in the middle of the door because when the landing gear is lowered or raised, there would be interference between the connecting rod and the landing gear, that is to say that the connecting rod would be given a movement such that the door would be pushed first of all and then pulled. This interference is due to the different movements of the landing gear as it is raised and lowered. Fitting the connecting rod at one end of the door would have the effect that most of the door would be free, that is to say unsupported, and that it would therefore be subjected to vibrations due to the movement of the aircraft. In addition, for the door to open sufficiently to allow the landing gear to pass, the door would need to open through a relatively large angle, and this would require the use of fittings for securing the door to the structure that have a large angular travel, for example large-sized goosenecks. However, if the gooseneck is large, the volume needed to house this gooseneck when the door is closed, is also large.